From 24f3478d664b1eaa6f8860d3aa521aebe51b2a62 Mon Sep 17 00:00:00 2001
From: Dan Williams <dan.j.williams@intel.com>
Date: Thu, 21 Dec 2017 17:04:07 -0800
Subject: [PATCH] ext4: auto disable dax instead of failing mount
Git-commit: 24f3478d664b1eaa6f8860d3aa521aebe51b2a62
Patch-mainline: v4.16-rc1
References: bsc#1104888 fate#325574

Bring the ext4 filesystem in line with xfs that only warns and continues
when the "-o dax" option is specified to mount and the backing device
does not support dax. This is in preparation for removing dax support
from devices that do not enable get_user_pages() operations on dax
mappings. In other words 'gup' support is required and configurations
that were using so called 'page-less' dax will be converted back to
using the page cache.

Removing the broken 'page-less' dax support is a pre-requisite for
removing the "EXPERIMENTAL" warning when mounting a filesystem in dax
mode.

Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Acked-by: Jan Kara <jack@suse.cz>

---
 fs/ext4/super.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 7c46693a14d7..18873ea89e08 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -3710,11 +3710,14 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 		if (ext4_has_feature_inline_data(sb)) {
 			ext4_msg(sb, KERN_ERR, "Cannot use DAX on a filesystem"
 					" that may contain inline data");
-			goto failed_mount;
+			sbi->s_mount_opt &= ~EXT4_MOUNT_DAX;
 		}
 		err = bdev_dax_supported(sb, blocksize);
-		if (err)
-			goto failed_mount;
+		if (err) {
+			ext4_msg(sb, KERN_ERR,
+				"DAX unsupported by block device. Turning off DAX.");
+			sbi->s_mount_opt &= ~EXT4_MOUNT_DAX;
+		}
 	}
 
 	if (ext4_has_feature_encrypt(sb) && es->s_encryption_level) {
-- 
2.16.4